Method of preparing metallic pigment pastes



Patented July 29, 1941 2,250,955 r oFFicE IWETHOD F PREPARING RETALLIC PIGMEN'E PASTEs Clarence P. Harris, New York, N. K, assignor, by mesne assignments, to United States Metal Powders, Inc., Baltimore, Md a corporation of Maryland No Drawing. Application Febrm 19, 1937, Se-

rial No. 126,638. Renewed .lianuary 10, 19M

6 Claims.

This invention relates to the production of metallic pigments in a form and condition convenient for mixing with the desired vehicle, which effects a more efiicient covering power of the metal powder, and substantially eliminates the dusting nuisance of metallic pigments in their customary powdered state.

This application is a continuation in part, of my co-pending application, Serial Number 755,- 635, entitled Production of metallic pigment paste, filed December 1, 1934.

So-called bronze powders consist of minute metallic particles, usually in flake form, this shape normally giving the greatest covering or opacitying effect and admitting of the maximum leafing properties. These powders vary in size of individual particles from about 200 to 325 mesh per inch, United States standard sieve, the individual particles of such powders dusting readily into the air, especially when they contain a large proportion of aluminum or other relatively light metal, being troublesome to handle, and dimcult to wet.

I have found that a powder of this character I may conveniently bemade into the form of a paste by mixing with it a solvent or solvent combination of the vehicle it is desired to employ,

in which condition, the dustnig property is eliminated, or at least reduced to a minimum whereby it becomes unobjectionable, and .the pigment mixes and incorporates readily with the vehicle.

Furthermore, the leaiing and/or covering power of the powder in the form of my well-balanced paste, exhibiting good physical and chemical stability, is greatly increased over that exhibited by the dry powder.

The leafing or covering power of the pigment is increased, or may be increased, by the present' invention, primarily because the metallic particles are completely separated from each other by the solvent which is used to form the paste, but the leafing power is not always synonymous with covering power.

The leafing power depends in a great measure upon the configuration and the surface condition of the individual metallic particles, especially asto the dimensions in respect to the weight per given cubical contents, and the ratio of one dimension in respect to another or to the others.

The covering power on the other hand, is greatly influenced in extent or degree by the absence of agglutination between particles, and the freedom of the individual particles in movement with respect to each other. This leafing characteristic is only evidenced, at least to any considerable extent, in certain types of media, and should not be confused with covering power. Maximum opacifying efiect is not synonymous with high leafing.

r This increase in leafing power, and especially in covering power or both, makes it easier to obtain a uniform distribution of the metallic particles throughout the viscous vehicle of the paint, lacquer, varnish, enamel or other type of protective coating.

By the term lacquer as herein used, it is to be understood as being almost universally applied to nitrocellulose or pyroxylin solutions, less often to acetated cellulose solutions, and of various types, either a nitrated or acetated cellulose as such, or a form of cellulose ester in conjunction with gums, resins, resinou bodies or products acting as such, and usually are highly viscous solutions in which it is diirlcult to incorporate a solid upon which the liquid portion of the lacquer has no solvent action, as with the metallic particles involved in. this invention. That is, with increased viscosity, comes decreased freedom of insoluble particle movement.

With "lacquers, the covering power maybe increased or not, while the leaflng properties in general are absent or of a very low degree, comparatively speaking. Usually the covering power and opacifying effect is materially augmented.

A more completely effective use of the metallic particles, as pigment, may thus be obtained for use in varnish vehicles or in lacquers, or compositions of this type, both by an increase in the leafing power, but especially by increase of covering power with no increase in leafing, and by increase of both leafing or covering power.

Metallic pigments in contact with organic liquids, especially the organic liquids normally employed in paint, lacquer, varnish, enamel and other types of protective coatings, usually accelerate decomposition of such liquids, and as such liquids or compositions contain organic acids in combination as the organic acid radicals of esters, free acids as normally present in gums and resins, and free acids liberated by decomposition of cellulose esters such as nitrated and acetated cellulose, metallic pigments therefore, are not mixed with their vehicles until immediately before use in order to minimize such decomposition. While the decomposition is usually more marked with the entire vehicle, decomposition also occurs with the solvent alone, especiallywhen the solvent contains esters as is usually the case, especially with such organic liquids as commercial mixtures of petroleum or other hydrocarbons, which are highly complex and variable as to the individual components therein and the degree of purity with which they are. found in commerce, such mixtures being frequently used as diluents of vehicles for metallic pigments.

This is especially so when these hydrocarbon mixtures contain small amounts of such impurities as sulfur and/or nitrogenous or other compounds, of varying degrees of stability,

and proneness to act one upon the other with the liberawhich ap- This decomposition of the solvent usually has a deleterious effect upon the brilliancy and extent of leaflng or leafing quality oi. the metallic powder, and sometimes modifies the covering power, probably by agglutinating or coalescing individual particles together, which appears explanable by the action of the acids liberated, or bodies of acid character liberated, which appear to act upon the surface of the metallic particle in such manner as to interfere with their free flowing and orientation in the liquid medium.

It is therefore a further object of the present invention to stabilize pastes or mixtures of metallic powders with organic solvents, or other lacquer, paint, varnish, enamel, etc., components. In accordance with the present invention, satisfactory degree of stabilization is attained by adding to mixtures of metallic powders with organic solvents, small amounts of materials which prevent or influence decomposition of the solvents.

The specific organic solvent or solvent combination employed for forming the paste of the present invention will depend in any instance upon the vehicle with which the paste is to be used, the'relative purity of the individual liquids or bodies comprising the solvent or solvent mixture, and possible incompatibility between solvent components, solids present as cellulose esters, cellulose ethers, gums, resins and resinous bodies.

For example, in case of many types of varnish,

I, it may be a petroleum fraction, as of the type of vamolene, or toluene, or xylene, or high flash solvent, naphtha (boiling between 150 and 200 centigrade) coal tar fraction, or tetrahydro naphthalene, a liquid synthetic product of about the same boiling range.

In each instance, however, the solvent employedjexerts solvent or colloiding action on the vehicle with which the pigment is to be applied, and usually constitutes at least part of the diluent of the vehicle.

Simple mixtures of the metallic powder with an organic liquid are likely to separate into layers of greater and lesser pigment content and concentration, so that the paste will lack the requisite homogeneity, and also there is proneness to agglutination of the individual metal particles with a corresponding diminution in covering power.

This is true even of pastes containing as much as 65% metallic powder incorporated therein. To prevent such a separation, or to minimize the same to a degree where it is commercially nonobjectionable, thickening agents which form true colloidal sols with the liquid, and which act as stabilizers, primarily in a physical sense, are employed. Such agents effectively maintain the initial homogeneity of the paste.

In accordance with one example of carrying out the present invention, the metallic powder is mixed, preferably mechanically with the solvent composition in which there has previously been dissolved or incorporated an alkali metal salt or alkaline salt of a relatively weak acid, such as anhydrous sodium stearate, sodium oleate, powdered anhydrous sodium silicate, sodium acetate, sodium butyrate, and the like. The alkali metal salts of the paraflin series of acids are especially applicable for this purpose, the sodium salts being used on account of their relative inexpensiveness.

Such salts or soaps will react with acids which appear to be formed by decomposition of the solvent present in the paste, thus preventing these acids from effecting further decomposition, and deleteriously acting upon the metal particle.

The reaction of the salt with they acids or bodies of acidic character or function formed in the decomposition liberates a very weak acid as stearic acid or silicic acid or the like, which has no obseryable deleterious action on the paste. Other substances which combine with impurities, and tend to prevent objectionable action on the metal particles may be used.

As a specific example of carrying out the present invention, 32 grams of polished aluminum powder are mixed mechanically with 17 grams of petroleum hydrocarbon distillate of the varnolene type, in which was previously dissolved 0.05 gram of anhydrous sodium stearate, or sodium oleate, or equivalent.

Alternately the same quantity of metal powder may be mixed with 17 grams petroleum distillate of "varnolene type boiling range, together with 0.05 gram of powdered anhydrous sodium silicate, sodium acetate, sodium butyrate, or

corporating therein a proportion of petroleum distillate of relatively high purity and required boiling range. The boiling range of the petroleum hydrocarbon fraction will vary considerably, depending upon the boiling range of the solvent portion, the proportion and speed of evaporation to cellulose ester, resin or other. lacquer solid portion.

The proportion-of solvent to non-solvent (usually a petroleum fraction or mixture of arcmatic hydrocarbons), portion is so adjusted, bearing in mind the boiling range and speed of evaporation of both solvent and non-solvent portion, so that there will be at no time during the evaporation phase, a suiiicient preponderance of non-sol'vent over solvent, so as to incipiently precipitate out the cellulose ester, and thereby decrease the tensile strength and other desirable properties of the final metallic-containing film.

In another representative example, I select an aluminum powder possessinglittle or no leafing quality. A cellulose ester solvent combination of suitable type is made, the following being representative:

. Parts Diethyl phthalate 5 Amyl stearate- 1 Butyl acetate (normal) 3 Crystallizable benzene 3 Absolute ethyl alcohol 3v The absolute ethyl alcohol is usual y above 99% ethanol.

Mix parts metal powder by weight with 25 to 35 parts of the above mixture by weight, adding 0.2 part urea acetate or equivalent nitrocellulose stabilizer. This paste is applicable for lacquering by'brushing by hand, by use of an air brush, or

for the coating of real leather, the production of artificial leather by the coating oi cloth, and the production of Spanish and old mission effects upon an artificial leather surface.

Or, I may prepare a cellulose ester solvent mixture relatively high in high boilers and therefore relatively slow evaporating, such, for example, as the following:

Parts Benzyl alcohol Benzyl acetate 2 Benzyl benzoate 1 Amyl benzoate /2 Cyclohexanol acetate 1 A further object of the present invention is to maintain uniformity of and in the paste, especially in the lacquer type of the same, and avoid separation into a more and a less fluid phase. For this purpose I employ dispersing agents, and I have found that some of the bodies above indicated form excellent dispersing and hence stabilizing agents for this purpose. I prefer such dispersing agents to be neutral materials, such as aluminum stearate, calcium stearate and similar materials. These likewise function to a more or less degree as stabilizing agents which normally increase the covering power in lacquer-type combinations.

As an exampleof the use of such a dispersing agent, 40 grams polished aluminum powder are mixed with 22 grams of a solution, preferably warm, made as follows:

200 grams purified petroleum distillate of varnolene boiling point range, and 4 grams sodium stearate.

The petroleum distillate and dispersing agent are preferably agitated until the latter passes into solution in the former.

I have described what I believe to be illustrations of some of the best embodiments of my invention. I do not wish, however, to be confined to the embodiments herein described, but what I desire to cover by Letters Patent is set forth in the appended claims.

What I claim is:

1. Metallic pigment paste consisting of a paste formed of metallic powder mixed with a solvent consisting of ethyl butyrate for vehicles used in protective coatings and a stabilizing agent for reacting with acids formed by the decomposition of the solvent by the powder to liberate a fatty acid having no appreciable deleterious effect on the paste, said stabilizing agent consisting of an alkali metal salt of a fatty acid.

2. Method for increasing the covering power of a protecting coating of the lacquer type containing a plurality of metal particles in leaf form, comprising incorporating with said particles a suitable lacquer solvent containing dissolved therein a metal salt of an acid selected from the group consisting of sodium acetate, sodium propionate, sodium butyrate, sodium oleate, and sodium stearate.

3. Method for increasing the covering power of a protecting coating of the lacquer type containing a plurality of metal particles in leafiorm, comprising incorporating with said particles a suitable lacquer solvent consisting of ethyl butyrate containing dissolved therein an alkali meta1 salt of 'a fatty acid.

4. Method for maintaining the uniformity ,of a protective coating of lacquer type containing metal flakes therein and in paste form, comprising incorporating with said metal flakes a solvent consisting of ethyl propionate containing dissolved therein a stabilizing agent for reacting with acids formed by the decomposition of the solvent to liberate a weak acid having no deleterious effect on the paste, said stabilizing agent comprising an alkali metal salt of an aliphatic.

5. A metallic pigment paste comprising minute metallic particles mixed with liquid ethyl propionate and a stabilizing agent for reacting with acids formed by the decomposition of the liquid by the metal particles to liberate an acid having no appreciable deleterious effect on the paste, said stabilizing agent consisting of sodium propionate.

6. A pigment composition comprising a mixture of metallic powder, an alkyl ester of an aliphatic acid, and an alkali metal salt of a weak aliphatic acid, the alkyl ester being one adapted to develop acidity in the pigment composition and the said salt consisting of an alkali metal salt of an acid selected from the group consisting of acetic, propionic, and butyric acids.

CLARENCE P. HARRIS.

CERTIFICATE OF CORRECTION. Patent 0. 2,2 0,95 July 29, 191p.

CLARENCE P. HARRIS.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction es follows: P ge 5, second column, line 56, claim 14., after "aliphatic" insert the word --acid-; and that the said Letters Patent should be read with this correction therein that the same. may conform to the record of the case in the Patent office.

Signed and sealed this 9th day of September, A. D. 19h1.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

